You’re confusing science fiction with reality here. Attacking a country with an asteroid would be an absurdly slow process without engines which are already weapons on their own. It’s like declaring you’re going to launch a full scale nuclear strike in 6 years and not a moment sooner, you spend all these resources which don’t help you until after you’ve lost the war.
The space race had little to do with the collapse of the Soviet Union, for one thing the timing is off significantly. The Soviet union mostly failed due to internal issues that were only tangentially related to the US. Excess military spending was more a symptom than an underlying cause, you can just as easily blame poor manufacturing becoming an increasing issue as technology advances, a culture of mismanagement etc. Corruption, infighting, apathy, ethnic tensions, mismanagement, etc all kept compounding until you got societal collapse.
The space race had little to do with the collapse of the Soviet Union, for one thing the timing is off significantly. The Soviet union mostly failed due to internal issues that were only tangentially related to the US. Excess military spending was more a symptom than an underlying cause, you can just as easily blame poor manufacturing becoming an increasing issue as technology advances, a culture of mismanagement etc. Corruption, infighting, apathy, ethnic tensions, mismanagement, etc all kept compounding until you got societal collapse.